Computer modelling studies of drug effects in vitro are in progress. In vitro studies on cytosine arabinoside, adriamycin, colcemid and cytochalasin B, and two dose schedule optimization studies employing ara-C and hydroxyurea are in progress. In vivo studies on the effects of hydroxyurea in mouse bone marrow are also in progress. Preliminary observations suggest that recruitment predominates over synchronization during recovery. Flow microfluorometry (FMF) studies have established the T lymphocyte as a useful diploid reference standard. FMF studies on the non-Hodgkin's lymphomas and on the ploidy of a variety of human solid tumors are ongoing. Tumor doubling times were measured in small cell carcinoma of the lung. A review of tumor doubling times in human solid tumors in relation to responsiveness to therapy and curability was completed. BIBLIOGRAPHIC REFERENCE: Bunn, P. A., Shackney, S. E., and Ford, S. S. Effects of Colcemid on Hematopoiesis in the mouse. J. Clin. Invest. 58: 1280-1285, 1976.